| Summary: | As an environmentally friendly gas with good insulation and stable chemical properties, CF<sub>3</sub>I gas mixture is considered as a potential alternative to SF<sub>6</sub> gas to compensate for the shortcomings of SF<sub>6</sub> gas as a greenhouse gas. This article attempts to study the CF<sub>3</sub>I ternary gas mixtures with c-C<sub>4</sub>F<sub>8</sub> and N<sub>2</sub> by considering the process of streamer development in surface discharge. The model of surface discharge in CF<sub>3</sub>I gas mixture under DC voltage was established by COMSOL, and the drift-diffusion equations of particles was solved to show the discharge process, and the changes of electric field and particle concentration, etc. during the development of streamer were obtained, which provides the theoretical basis for the reliable diagnosis of partial discharge. On this basis, the model is compared with models for two other different gases (SF<sub>6</sub>/N<sub>2</sub>, artificial air) in terms of particle characteristics, streamer characteristics and streamer branches characteristics. Finally, it is concluded that under this model, although the insulation characteristics in CF<sub>3</sub>I gas mixture are weaker than those in SF<sub>6</sub>, the difference is not large and both are much better than those in artificial air, so c-C<sub>4</sub>F<sub>8</sub>/CF<sub>3</sub>I can be considered as a potential substitute for SF<sub>6</sub>.
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